1. Field of the Invention
The present invention relates to a polyphenylene ether based thermoplastic molding resin.
2. Description of the Background
Polyphenylene ethers (PPE) are technical high performance thermoplastic materials which have high melt viscosities and softening points. They are therefore suitable in numerous technical applications in which stability at high temperatures is important (see U.S. Pat. Nos. 3,306,874, 3,306,875, 3,257,357 and 3,257,358). However, certain properties of polyphenylene ethers make the same undesirable in many technical applications. For example, molded parts of polyphenylene ethers are brittle, because of their poor impact resistance.
The high melt viscosities and softening points of PPEs, which lead to processing difficulties, are detrimental. Further, consideration must be given to the fact that polyphenylene ethers tend to be unstable and discolor at high temperatures.
Another characteristic of polyphenylene ethers is that they are soluble in many organic solvents or swell to a large extend. This means that PPEs are unsuitable in applications where they would as a matter of course come into contact with solvents.
Another characteristic of polyphenylene ether resins is that the properties of PPEs can be improved by mixing PPE with other polymers. Thus, e.g., blends of PPE with impact-resistant polystyrenes have attained substantial technical importance (see German Pat. Nos. 2,119,301 and 2,211,005). These resin compounds can be readily processed into molded parts which have sufficient impact-resistance. However, the compounded material has the disadvantage that with increasing polystyrene content, the heat distortion temperature of the blends decreases when tested. These resin blends also, however, have unsatisfactory solvent resistance.
Compound blends of polyphenylene ethers and polyamides exhibit good flowability (see examined German patent application No. 1,694,290 and JP-A No. 7,847,390). However, such resin blends are usually brittle materials, because the two components are incompatible and are poorly dispersable in each other. Aromatic polyamides, such as the types which have been used and which are described, for example, in European unexamined patent application No. 0,131,445, have poor processability with polyphenylene ethers. However, better compatibility of both phases can be achieved by functionalizing the polyphenylene ether component, e.g., with maleic anhydride, in the presence of a radical initiator (J No. 5,906,452). However, the use of a radical initiator leads to an undesirable and uncontrolled partial gelling of the PPE-phase.
In view of the above stated compatability problems of PPE-polyamide, it has been suggested that the compatibility of both polymers can be increased by adding a sufficient quantity of a lubricant such as an organic phosphate (see European unexamined patent application No. 0,129,825) or a diamide (see European unexamined patent application No. 0,115,218) to the resin blends. However, this attempted solution to the problem is not satisfactory, because, although improved compatibility is achieved, the resin blend exhibits considerably reduced heat distortion temperature.
The same disadvantages are characteristic of molding compounds to which copolymers of styrene and unsaturated acid derivatives have been added (see European unexamined patent application No. 0,046,040).
Another reference, which is European Pat. No. 0,024,120, discloses resinous compound blends which are composed of a polyphenylene ether, a polyamide, a third component and, appropriately, a high-molecular caoutchouc polymer. Suitable third components include liquid diene-polymers, epoxy resins or a compound having a double or triple bond and a functional group such as an acid, anhydride, ester, amino or alcohol group. However, the impact resistance of the resinous compound which is obtained is insufficient for many applications. A need therefore continues to exist for a molding composition based on polyphenylene ether which is readily processible and which exhibits improved properties.